The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is driven by several turbojet engines each housed in a nacelle channeling the air flows generated by the turbojet engine, this nacelle generally housing a mechanical thrust reversal system.
The role of a thrust reverser, upon touchdown of an aircraft, is to improve the braking ability of the aircraft by redirecting forward at least a portion of the thrust generated by the turbojet engine, which adds to the wheel braking of the aircraft.
The means implemented to achieve this cold flow redirection vary depending on the type of reverser. However, in all cases, the structure of a reverser comprises mobile cowls movable between a so-called “direct jet” or closed position, wherein they close this passage and a so-called “reverse jet” or open position, wherein they open a passage for the diverted flow within the nacelle.
In the case of a grid-type thrust reverser for example, also known as cascade thrust reverser, redirecting the air flow is performed by cascades, the mobile cowl having a mere sliding function to cover or uncover these grids.
The translation of the mobile cowl is carried out along a longitudinal axis substantially parallel to the axis of the nacelle. Thrust reversal flaps, actuated by the sliding of the cowl, make it possible to block the cold flow stream downstream of the cascades, such as to optimize the redirection of the cold flow to the outside of the nacelle.
Moving such a mobile cowl is commonly obtained by means of mechanical actuators such as that disclosed in application PCT/US2004/019260, and which has been represented in FIG. 1 attached.
It is worth noting that such an actuator can be either hydraulically (hydraulic-mechanical actuator) or electrically (electrical-mechanical actuator) powered.
Such a mechanical actuator comprises a worm drive 1 whereon a nut 3 is screwed, the latter being secured to an extension tube 5 with an eyelet 7 at its free end.
In one form, balls 8 are interposed between the threads of the screw 1 and those of the nut 3 such as to reduce friction, thus, this type of actuator is commonly referred to as “ball screw”.
The screw 1 comprises at the end opposite to that of the eyelet 7, a pinion 9 with conical teeth cooperating with a master pinion 11 the latter being directly or indirectly driven by rotational drive means such as an electric motor.
Under the action of this electric motor, the screw 1 may be swiveled in one direction or the other, and thus translate the nut 3 in one direction or the other, hence, extending or retracting the tube 5.
These movements of the tube 5 make it possible, by means of its eyelet 7, to act on the movable member of the nacelle such as a mobile cowl of grid-type thrust reverser (considering that there are usually several actuators of this type to move such a mobile cowl).
More specifically, as is visible in FIG. 2, the eyelet 7 cooperates with a clevis 15 secured to the mobile cowl of the thrust reverser (not represented), this eyelet being connected to this clevis by a bolted screw 17.
In order to prevent an untimely deployment of the mobile cowl of the thrust reverser, safety locking means are typically provided, which must be deactivated prior to any thrust reversal operation.
These locking means particularly comprise primary locking means, commonly designated as PLS (Primary Locking System).
This PLS system, represented generically by box 19 on FIG. 1, comprises a locking rod capable of blocking the rotation of the drive shaft 12 of the master pinion 11, it is worth noting herein that the drive shaft itself is driven in rotation by flexible transmission shafts commonly called Flexshafts.
Such a PLS system is known for example from document U.S. Pat. No. 4,586,329, or from document U.S. Pat. No. 6,487,846.
As is visible in each of the devices disclosed in these documents, the design of the PLS system is complex: at its end the locking rod comprises a locking bar, pivotally and slidingly mounted on this finger, the ends of this locking bar being capable of cooperating with two abutments arranged at 180° on the drive shaft of the master pinion.